SoftetherVPN is already available as a package but.... this is a rather large but, the version that's available is quite old and doesn't seem to be getting any attention from it's packager. There is also no GUI for this but it's fairly trivial to configure manually and there is s management package but it's Windows.

I use SoftEtherVPN and prefer to run it on an internal server because of the outdated package, I build it myself on a CentOS7 server, can you run it on an internal server or would you prefer to run it on OPNsense?

I would prefer to run it on OPNsense (as a complete openvpn substitute) but at this moment I can also use an another machine: but in my case I don't need SoftEther server but only as the client version.

So I could use a VPS with SoftEther server (and Softether client on a my internal machine) or I can use a VPN provider compatible with Softether: what do you think?

At this moment I use OPNSense as VPN gateway to VPN Internet provider (like StrongVPN, AirVPN, ExpressVPN and so on): I configured OPNSense (firewall outbound with specific rules) to use this VPN connection from some (but not all) LAN hosts.

I would like to substitute Openvpn with softether on opnsense: at this moment I think is not possible. Am i right?

Maybe I must to install Softether client on a Linux host and use it as gateway for every LAN hosts that need a VPN connection.

As I mentioned, the current Softether server software is quite old an you may want to consider building it for OPNsense but as I'm not experienced enough for that I don't know if it's worthwhile, it's a pity the packager doesn't keep pity up to date.